1. Field of the Invention
The present invention relates to a magnetic head used for writing and reading data in and from a magneto-optical disk by utilizing Magnetically-induced Super Resolution (MSR for short) method.
2. Description of the Related Art
The MSR method is one of the techniques used for enabling proper reading operation of adjacent record marks which, with a resolution determined by the diameter of the laser spot, may fail to be recognized as separate marks An magneto-optical disk to be read by this method may include a plurality of magnetic layers whose magnetic characteristics can be varied depending on temperature. In operation, the data stored in the disk (or record marks stored in a recording layer of the magneto-optical disk) will be read out from an area of the laser spot which has a particular temperature.
More specifically, according to the MSR method, a laser beam is emitted onto the magneto-optical disk being rotated, and the laser beam forms a bright spot on the disk. As a result, a particular area of the disk is heated up, thereby dividing the disk into a relatively high temperature region and a relatively low temperature region. (As can be easily understood, the dividing manner described here is just an example, and the disk may be divided into three or more regions based on difference in temperature.)
Typically, the relatively high temperature region becomes elliptic in configuration (as viewed from above) to extend downstream of the laser spot. On the other hand, the relatively low temperature region is situated around the relatively high temperature region.
When the two regions of different temperatures are thus provided, one of the magnetic layers of the magneto-optical disk (an intermediate magnetic layer for example) will have its magnetic characteristics altered at a portion corresponding to the relatively high temperature region of the disk (or to the relatively low temperature region, alternatively).
As a result, this particular magnetic layer, which has its magnetic properties partially altered, works as a mask for shielding some of the record marks in the laser spot. Then, the magnetic information of the non-shielded record marks is transferred to the regeneration layer of the disk and will be read out optically.
The MSR technique described above has several variations. Among them are RAD (Rear Aperture Detection) method, FAD (Front Aperture Detection) method, D-RAD (Double mask RAD) method and CAD (Center Aperture Detection) method. In the first three methods (RAD, FAD and D-RAD), use is made of a magnetic film with perpendicular magnetization for the regeneration layer of the disk, whereas the last method (CAD) utilizes a magnetic film with horizontal magnetization for the regeneration layer. In the magnetic film with horizontal magnetization, the direction of magnetization is horizontal at room temperature, but the direction may be turned to be perpendicular when the film is heated up to a temperature of 100 to 150.degree. C.
According to the RAD method, the relatively low temperature region is masked, and data will be read out from the relatively high temperature region. On the other hand, by the FAD, data are to be read out from the relatively low temperature region, with the relatively high temperature region being masked. By D-RAD, both the relatively high and low temperature regions are masked, so that data will be read out from an intermediate temperature region. By the CAD, the relatively low temperature region will be masked.
Each of the RAD, the FAD and the D-RAD requires that the regeneration layer of the magneto-optical disk be magnetically initialized (alignment of magnetization) before the magnetic information is transferred from the recording layer to the regeneration layer. Thus, in order to employ any one of the above three methods for performing data-reading, it is necessary to provide both a regenerating magnetic field generator and an initializing magnetic field generator.
The regenerating magnetic field generator may be located at a position corresponding to the laser spot, while the initializing magnetic field generator may be located at a position spaced upstream from the laser spot. When the CAD method is utilized, an initializing magnetic field generator is not necessary because the magnetic film with horizontal magnetization is used for the regeneration layer. (As the temperature decreases, the direction of the magnetization of the magnetic film is changed from the perpendicular one to the horizontal one. This means that the initialization of the magnetic film is automatically performed with the fall of the temperature.) Actually, when the CAD method is used, no initializing magnetic field generator should be provided, so that the magnetic condition of the magnetic film can be prevented from being disturbed by an external magnetic field.
Turning now to a data-writing operation for the magneto-optical disk, a laser beam is emitted onto the disk while an external magnetic field having a predetermined direction is being applied to the recording layer. When the temperature of a portion of the recording layer is raised above the Curie temperature by the laser beam, the direction of the magnetization of that particular portion is reversed, which means that data are stored.
As described above, a disk apparatus capable of reading and writing data from and in a magneto-optical disk needs both an optical head for emitting a laser beam onto the disk and a magnetic head for generating magnetic fields to perform data-storage, data-reading and disk-initializing operations. Typically, the optical head is held in facing relation to the recording surface of the disk, while the magnetic head is arranged opposite to the optical head with respect to the magneto-optical disk.
In this connection, JP-A-7(1995)-326086 for example discloses, as shown in FIG. 5 of the document, a bias magnet (07) for generating a magnetic field to perform data-reading and data-writing, and an initializing magnet (09) carried by a slider (08a). The initializing magnet (09) is a permanent magnet.
With the disclosed arrangement, the bias magnet (07) and the initializing magnet (09) are separately supported by different supporting members. The problem of such an arrangement is that the supporting structure for the two magnets tends to be complicated, thereby making the assembly and/or maintenance of the supporting structure rather difficult. Further, since the initializing magnet (09) is a permanent magnet, the CAD method cannot be used for the disclosed apparatus.
JP-A-6(1994)-131738 discloses, as shown in FIG. 6 of the document, a magnet head device including a bias magnet (41) and a slider (37) carrying the bias magnet. The slider (37), however, is not provided with an initializing magnet. Thus, an initializing means may need to be separately prepared, which makes it difficult to reduce the size of the magnetic head device (and consequently, the size of the entire magneto-optical disk apparatus).